A conventional winding cone includes both a frusto-conical surface for receiving and retaining an end of a torsion spring and a base having an opening therein for receiving a set screw whereby the end of the spring is fixed to a torsion rod extending axially through the winding cone. With this type of winding cone, the force of the spring does not have to be overcome prior to releasing the set screw. The set screw can simply be released without regard to the torque of the torsion spring on the winding cone. Consequently, an inexperienced person often will release the set screw without sufficiently bracing against the torque of the torsion spring thereby leading to unexpected and rapid unwinding of the torsion spring and possible injury. A need therefore exists for a failsafe whereby the torque of the torsion spring must first be overcome before the securement of the torsion spring to the torsion rod by the set screw can be released.
Balk U.S. Pat. No. 5,671,500 is illustrative of a conventional torsion spring assembly used in a counterbalancing mechanism for an overhead door. The torsion spring 3 is axially disposed about torsion rod 20. One end of the spring is retained by cone 16 that is mounted to the rod 20 by adjustable mounting 18, and the other end of the spring is retained by cone and bracket 12 which are rotationally fixed relative to rod 20. Rotation of rod 20 causes rotation of mounting 18, cone 16, and torsion spring 3 leading to a change in the tension of the torsion spring 3. The tension range is adjusted by: first releasing a set screw which fixes mounting 18 to rod 20; next rotating mounting 18, cone 16, and spring 3 relative to the rod 20 in the desired direction; and then re-engaging the set screw with the rod 20 through the mounting 18. No failsafe is provided to insure that the tension in torsion spring 3 will be maintained when the set screw is released from torsion rod 20.
With more particular detail to the conventional structure of a winding cone itself, Martin U.S. Pat. No. 4,817,927 discloses in FIG. 4 a winding cone 60 and, in FIG. 3, an anchor cone 10. A tool (not shown) is inserted into apertures 68 or 69 for selectively adjusting the tension in the torsion spring 50 and set screws are provided through aperture 64 in base 62 for mounting the winding cone to the torsion rod 34. Martin provides markings on the winding cones to indicate which direction each cone should be rotated to wind the torsion spring 50. Similarly, Kalister U.S. Pat. No. 3,779,537 discloses a winding cone and winding base that includes both left-hand and right-hand threads for receiving either a left-hand or right-hand wound spring. Similar to Martin, the winding cone is secured to the torsion rod by set screws. The winding cones of both of these references fail to provide a failsafe for insuring that the torque of the torsion spring is adequately braced against when the winding cone is released from the torsion rod for winding of the torsion spring.
Apart from the structure of a torsion spring assembly or a winding cone, Way U.S. Pat. No. 5,605,079 actually relates to a device for rotating the winding cone and winding the torsion spring for increasing winding tension. In particular, Way discloses a housing that is mountable to a winding cone to which ratchet arms are attachable for increasing the tension in the torsion spring. In using the device, a ratchet arm must be braced to counteract the force of the torsion spring that is released when the set screw is removed. In Way no failsafe is provided whereby the spring force must first be overcome before disengagement of the set screw. In fact, the opening 66 by which the set screw is accessible is continuously aligned with the set screw 34 and the housing 36 in which the opening is formed is fixed to the winding cone. Thus, the set screw is continuously accessible in the device of Way.
The prior art also includes devices for adjusting the operating tension range in a torsion spring assembly which does not involve the rotation of the winding cone relative to the torsion rod and, thus, does not include the dismounting of the winding cone from the torsion rod to which the failsafe of the present invention relates. Such devices are disclosed, for example, by Davis U.S. Pat. No. 4,882,806; Carper et al. U.S. Pat. Nos. 5,636,678 and 5,632,063; and Husselton U.S. Pat. No. 5,239,777. None of these mechanisms relate to the winding of the torsion spring by rotation of the winding cone relative to the torsion shaft, nor do they provide a safeguard against an inadequate force bracing against the release of the torsion spring tension.
Looking beyond overhead doors to the art of spring hinges, a few references relate to the adjustment of the tension in torsion springs thereof. In Rapp U.S. Pat. No. 4,817,242, a spring hinge for a toilet seat is disclosed wherein the tension in the torsion spring is adjustable. Specifically, Rapp discloses, with relevance to the present invention, a torsion spring 2 axially disposed about a rod 1 within a hinge. A first end of the torsion spring 2 is secured to end cap 9 and a second end of the torsion spring is secured to a first coupling member 6 that is mounted to the rod 1 and that has teeth which interlock with a second coupling member 5. End cap 9 is mounted to the toilet and second coupling member 5 is mounted to the seat. The first coupling member 6, and the second coupling member 5, when interlocked therewith, are rotational with the rod 1 relative to end cap 9, which rotation increases and decreases the tension in torsion spring 2 within a certain range. This range of tension is adjusted by: first axially moving the first coupling member 6 away from the second coupling member 5 into an unlocked position by axially displacing rod 1 against the spring force via knob 8 thereby compressing the spring; then rotating the first coupling member 6 and the spring 2 attached thereto relative to the second coupling member 5 by rotating rod 1 via knob 8; and then moving the first coupling member 6 back into interlocking relation with the second coupling member 5 by releasing the knob 8.
Curry et al. U.S. Pat. No. 4,073,038 discloses a spring hinge in which the torsion spring 23 biasing the hinge has a selectable tension range. In particular, torsion spring 23 is retained between cone 22 fixed to hinge 12 via set screw 35, and cone 24 coupled to plug 20 which, in turn, is fixed to hinge 11 via set screw 32. The coupling between cone 24 and plug 20 is accomplished through mating engagement surfaces 26,27. When the tension range is to be adjusted, a wrench 29 is inserted through an opening in the plug 20 into an opening 28 in cone 24. Due to the contoured engagement surfaces 26,27, rotation of the wrench about the axis of the torsion spring 23 in a first direction will cause the cone 24 and plug 20 to rotate relative to one another in segmented increments. However, the contoured engagement surfaces 26,27 prevent the rotation of the cone 24 and plug 20 in the segmented steps in the opposite direction unless the cone 24 and plug 20 are separated by an axial force applied directly to the cone 24 via the wrench 29.
Hwang U.S. Pat. No. 5,048,155 discloses a spring hinge in which the torsion spring biasing the hinge has an adjustable tension range. In particular, torsion spring 30 is retained between end cap 50, secured to a first hinge by set screw 90, and end cap 40 secured to a second hinge by set screw 70. A number of openings are formed in the second hinge member 10 and, in particular, in knuckle 12 in which the end cap 40 is disposed, through which set screw 70 can engage and retain end cap 40. A pin 83 and openings for the pin in knuckle 12 are also provided whereby the end cap 40 can be immobilized when set screw 70 is removed. Adjusting the tension range of the torsion spring with wrench is then possible once pin 83 holding the torsion spring against unwinding is removed; however, sufficient torque must be applied to the end cap 40 through wrench in order to overcome the frictional forces acting on the pin 83 due to the spring tension for withdrawal thereof through the opening.
As will be apparent, none of these references disclose or suggest a failsafe whereby the torque of a torsion spring in a torsion spring assembly of a counterbalancing mechanism of an overhead door must be overcome before the winding cone can be unsecured from the torsion rod.